Surging GlaciersSurging GlaciersHeike Bischof

6/8/2003

Trapridge Glacier, Yukon

Seminar OutlineSeminar Outline

Definition and Characteristics

The Surge Cycle

Example: Variegated Glacier

Drainage Systems and Glacier Flow

Two mechanisms based on two case studies

What are surging glaciers?What are surging glaciers?

Surge behaviour: “multi-year oscillation between

extended periods of normal motion and brief periods of comparatively fast motion.” (C.F.Raymond, 1987)

CharacteristicsCharacteristics

Globally small percentage (5%) Represtentation in varying climates Various types of glaciers can surge Surging glaciers surge in periodic cycles Clustered in some regions, mainly

Alaska, Yukon, British Columbia, Iceland, Svalbard (Arctic), Pamir

also: Antarctica, Spitsbergen, California, Andes Artic: Ellesmere and Axel Heiberg Island, Asia: Karakoram Mountains, Caucasus, Tien Shan

The Surge Cycle The Surge Cycle (Quiescent Phase)(Quiescent Phase)

Quiescent phase longer than active phase (up to 500y)

Filling and thickening of reservoir area Increase in creeping in reservoir area Stagnation and thinning in receiving

area Steepening front at Dynamic Balance

Line (DBL) (Raymond 1987)

Trapridge Glacier, Yukon

The Surge CycleThe Surge Cycle(Active Phase)(Active Phase)

Ice velocity increase of one magnitude Ice displacement 1/10 of glacier length Ice propagates in kinematic waves from

upper to lower glacier resulting in large elevation drops and rises (100-200m) Surge usually coincides with advance of the glacier terminus (steep, bulging front)

Hubbard Glacier

1982/3 Surges of Variegated 1982/3 Surges of Variegated Glacier…Glacier…continuedcontinued

(Benn and Evans, p.173)

1982/3 Surges of Variegated 1982/3 Surges of Variegated Glacier Glacier (Kamb et a., 1985)(Kamb et a., 1985)

The surge took place in different phases over 2y

Outburst floods coincide with

slowdowns in surge activity

At km 7: Ice thinning of 50m

At km 16: Ice thickening of 100m

Variegated Glacier

Presurge(July ‘82)

During Surge (July ’83)

How do glaciers move?How do glaciers move? - creeping (no water)

- internal deformation of the ice ( “ )

- bed deformation (subglacial water)

- basal sliding (subglacial water)

high speeds are achieved through sliding on a water lubricated base

Boreholes measurements: high water pressure coincides with an increase, floods with slowdowns in flow velocity during the active surge phase

Subglacial Drainage Subglacial Drainage SystemsSystems

Depends on water discharge, temperature distrubution , ice-bed interface, permeability, topography, rigidity of bed

Discrete water transported in a few channels organised drainage system, large volume

of water necessary Distributed systems

water transported over large proprotion of the bed

unorganised drainage system, little meltwater

Linked Cavity SystemLinked Cavity System(Variegated Glacier)(Variegated Glacier)

Summer meltwater is stored in cavities during winter

Spring ablation adds extra water establishing channels between cavities

Water drainage is slowed down as water is stored in cavities

Injection of tracer dye during surge average flow speed 0.02m/sec requires

the tunnel to be 1mm in diametre Measured discharge required for

diametre of 4.5m

Sliding on ‘hard beds’ Sliding on ‘hard beds’ (Kamb et al.,1985)(Kamb et al.,1985)

Water pressure in cavities rises When the water pressure comes close

to, or exceeds the overburden pressure, the glacier floats on a layer of water

Sliding occurs When the water pressure falls in

cavities, the glacier contacts the bed

Sliding stops

Sliding on ‘soft beds’Sliding on ‘soft beds’ (Clarke et al., 1984)(Clarke et al., 1984)

Traprigde Glacier is generally frozen to its bed, but at pressure melting point in upglacier-area

A drainage system is established in a permeable bed during the quiescent phase

During a surge, the drainage system might be destroyed temporarily, allowing pore pressure to build up and inducing shear failure of the substrate => Sliding/ Subsole deformation

DiscussionDiscussion

? How does inconsistency of flow velocity evolve?

? Why do only certain glaciers surge? Relationship to bedrock, topography

? Why are surging glaciers clustered in some areas?

? Only few studies have been undertaken on subpolar and cold based glaciers

ReferencesReferencesBenn, D.I. and D.J.A. Evans (1998) Glaciers and Glaciation, Oxford Universtiy

Press, Oxford. Bennet, M.R. and N.F. Glasser (1997) Glacial Geology – Ice Sheets and

Landfroms, John Wiley and Sons, Chichester.Clarke, G.K.C. et al. (1984) “Flow, thermal structure, and subglacial

conditions of a surge-type glacier” in Can.J.Earth.Sc.21 pp.232-240.Fatland, D.R. and C.S. Lingle (2002) “In SAT abservations of the 1993-1995

Bering Galcier(Alaska U.S.A.) surge and a surge hypothesis” in J.Glaciol.48 pp.439-451.

Kamb, B. (1985) “Glacier Surge Mechanism: 1982-1983 Surge of Variegated Glacier, Alaska” in Sc.227 pp.469-479.

Kamb, B. (1987) “Glacier Surge Mechanism Based on Linked Cavity Configuration of the Basal Water Conduit System” in J.Geophysical Research 92 pp.9083-9100.

Meier, M.F. and A. Post (1969) “What are glacier surges?” in Can.J.Earth Sc. 6 pp.807-17.

Raymond, C.F. (1987) “How do glaciers surge? A Review?” in J. Geophysical Research 92 pp.9121-9134.